Melt processable perfluoropolymers such as tetrafluoroethylene/perfluoro(alkyl vinyl ether) (PFA), tetrafluoroethylene/hexafluoropropylene (FEP), tetrafluoroethylene/hexafluoropropylene, and perfluoro(alkyl vinyl ether) are processed in the melt by methods such as extrusion molding, blow molding, injection molding, and rotomolding. The resulting molded articles have good high temperature properties, chemical resistance, low coefficients of friction, flame resistance, and good electrical properties (low dielectric, low dissipation). However, perfluoropolymers have lower dynamic physical properties than do partially fluorinated fluoropolymers showing polarity such as polyvinylidene fluoride (PVDF), ethylene/tetrafluoroethylene (ETFE) and polychlorotrifluoroethylene (PCTFE). Unlike the partially fluorinated fluoropolymers, which have intermolecular interaction, in perfluoropolymers there is almost no attraction between polymer molecules (chains) (Modern Fluoropolymers, John Wiley & Sons, NY, 1997, pp. 5-66). Further, the dynamic physical properties, such as elasticity, suffer reduction at temperatures greater than or equal to the glass transition temperature. The glass transition temperature (α transition temperature) of the perfluoropolymers is generally 120° C. or lower. Additionally, perfluoropolymers are flame-resistant, but when exposed to the heat of a fire, melt and can flow, resulting in high-temperature liquid droplets that generate smoke and can spread fire.
U.S. Pat. No. 6,177,518 discloses that the heat distortion temperature and elasticity of perfluoropolymers are improved by blending the perfluoropolymers with polyether ketone. However, this improvement in dynamic physical properties at high temperature is achieved at the sacrifice of a part of perfluorinated character (e.g., chemical resistance, electrical properties) of the fluoropolymers since 30% or more of polyether ketone is blended with perfluoropolymers.
Recently, techniques have been proposed for improving the mechanical characteristics (e.g. heat distortion temperature, chemical resistance, gas permeability) by directly melt-mixing polymers with inorganic fine particles. If inorganic fine particles are melt-mixed in polymers, however, the cohesive force of the inorganic particulates increases as the particle diameter decreases, causing re-agglomeration of the particles to occur. Therefore, it is extremely difficult to disperse inorganic fine particles at the nanoparticles level in polymers (47th Material Research Combinational Lecture Meeting, Science Council of Japan, Vol. 47, p. 150, 2003).
In reports on techniques for nanodispersing organically processed layered-silicates in polymer materials to solve these problems, in many cases the polymers used are polar polymers such as polyamide perfluoropolymers (Advanced Polymer Science, p. 135, 2005). In attempts to organically disperse processed layered-silicates in fluoropolymers, nanodispersing was successful in partially fluorinated fluoropolymers such as polyvinylidene fluoride (PVDF), which as noted above have polarity and show intermolecular interaction, but not in perfluoropolymers such as THE/HFP copolymers (FEP) (Journal of Applied Polymer Science, vol. 92, p. 1061, 2004). Further, in Kokai Patent 2000-204214, fluoropolymer nanocomposites obtained by melt-mixing mainly fluorine-containing rubber with organically processed layered-silicates are described, but there is no description of perfluoropolymers being so treated.
U.S. Pat. No. 5,962,553 discloses the melt-mixing of organophosphonium-treated layered-silicates with perfluoropolymers to improve dynamic physical properties. But, there is no evidence such as X-ray measurement or electron microscope observation to confirm the nano-dispersion of the layered-silicates in the perfluoropolymers. The elastic modulus of the resulting perfluoropolymer composites is greater than that of the perfluoropolymer itself by no more than two times. Furthermore, because the layered-silicates are processed with organophosphonium, the chemical resistance and high temperature properties of the resulting perfluoropolymer composites are less than that of the perfluoropolymer itself.
WO 2004/074371 discloses that the physical properties such as gas and chemical impermeability and elasticity, of melt processable fluoropolymers are improved by adding both organophosphonium-treated layered-silicates and functional group-containing melt processable fluoropolymers to melt processable fluoropolymers and melt-mixing. For example, the storage elasticity at room temperature is about twice that of the fluoropolymer itself. However, since functional group-containing melt processable fluoropolymers in addition to organophosphonium-treated layered-silicates are contained, however, the heat resistance of the resulting perfluoropolymer composites is reduced. There is also an economic penalty due to the use of expensive functional group-containing melt processable fluoropolymers.
U.S. Patent Application No. 2003/0228463 discloses that fluoropolymer composites obtained by nanodispersing layered-silicates without organic treatment in fluoropolymers such as polychlorotrifluoroethylene (PCTFE), have improved dynamic physical properties and storage elasticity at room temperature and at temperatures of 100° C. or higher. The good chemical resistance and heat resistance of the fluoropolymer itself is retained. The perfluoropolymer composites are obtained by mixing aqueous fluoropolymer dispersions of for example, PCTFE, with dispersions of layered-silicates having no organic treatment and then by precipitating, separating and drying of the solid phase of the resulting mixed aqueous solutions. The high temperature (150° C.) storage elasticity of the fluoropolymer composites showing polarity like PCTFE was increased about 2.5 times as compared to that of the fluoropolymer itself. However, but there is no disclosure as to whether the improvement of storage elasticity could be obtained in perfluoropolymers that have no polarity, and therefore no intermolecular interaction. The procedure of blending dispersions of nanodispersing layered-silicates and fluoropolymer dispersions followed by precipitating, separating and drying the solid phase of aqueous mixed solution, has also been reported in Chinese Laid Open Patent CN 1238353A and Journal of Applied Polymer Science, vol. 78, p. 1873 ff, p. 1879 ff, 2000.
Because of their superior electrical properties and heat and flame resistance, perfluoropolymers are widely used as insulation and jacket materials of communication cables (plenum cable). In these perfluoropolymers for communication cables, the extrudability onto the wire (conductor) improves as the melt viscosity decreases (i.e., as the melt flow rate increases). However, communication cables insulated with perfluoropolymers having low melt viscosity are at risk of dripping molten polymer when a fire breaks out, causing smoke generation and spread of the fire. To prevent fire propagation caused by cable insulation, the flame resistance standards are in place, as for example the US NPFA-255 standards. Accordingly, perfluoropolymers are needed that, in electric wire extrusion, have low viscosity and therefore superior processability (e.g. speed) on wire coating lines, but which on the other hand have high viscosity at low shear rate such as under the influence of gravity, so that the wire insulation does not drip when exposed to fire temperatures.
Perfluoropolymer compositions resistant to dripping when exposed to fire have been made by blending perfluoropolymers with a large amount of inorganic fillers, such as 10-60% of zinc oxide, and a small amount of hydrocarbon polymers for preventing deterioration of physical properties (U.S. Patent Application No. 2005/0187328). However, other properties of perfluoropolymers are compromised by the use of large amounts of inorganic fillers such as zinc oxide. Further, since zinc oxide and perfluoropolymers are directly melt-blended, conventional microcomposites having poor high-speed extrudability are obtained. They are not nanocomposites.
There is a need for perfluoropolymers having low viscosity at high shear and high viscosity at low shear, that also maintain good storage elasticity above their glass transition temperatures, without the addition of excessive amounts of filler.